Telephone cable is generally composed of three basic parts, a core, a shield and a jacket. In "PIC" telephone cable (Polyethylene insulated cable), the jacket is made of extruded polyolefins (usually polyethylene) and the core is made up of a plurality of insulated electrical conductors, the insulation usually being made of the same or similar material as the jacket. The jacket (usually an outer jacket) normally contains a significant amount of carbon black. It is thought that because of this carbon black, exposure of a polyethylene jacket to the atmospheric elements, particularly sunlight, does not significantly result in its degradation. On the other hand, this is not the case with the insulated electrical conductors that make up the core. They ordinarily contain a pigment other than carbon black.
For the purpose of identification, it is desirable and the usual practice is to have different colors of insulation for the insulated electrical conductors that make up the cable core. Except for the color black (usually derived from carbon black), it has been found that when exposure to atmospheric elements, the polyolefin, e.g., polyethylene, used for the conductor insulation, significantly deteriorates (splits, cracks, embrittles) over a period of time. Since each and every one of these insulated conductors, except the black ones, contain Rutile (Ti0.sub.2) it has been advanced that Rutile contributes towards this tendency to degrade in most environments.
To combat this degradation, attempts have been made to stabilize the insulation on the conductors with what is known as an antioxidant. An example of such antioxidant is a material sold underneath the trademark "SANTONOX" and is chemically known as 4,4' thiobis (6-tertiary butyl-3-methyl phenol). Prior to 1959, this antioxidant was used at 0.05% by weight concentration and after the middle of 1962, 0.1% by weight. In all known cases to date, this antioxidant has been mixed in with the polyethylene and such mixture extruded simultaneously while the insulation was being placed on the conductors. Another example of an antioxidant is tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamated)] methane, sold under the trade name IRGANOX-1010.
For the purpose of this disclosure and appended claims, the term antioxidant is used herein to mean any chemical component normally existing in the solid state at conditions of standard temperature and pressure (STP) that will neutralize or otherwise combine with to so neutralize free radicals and/or ionization products that a polyolefinic polymer would otherwise form under conditions other than and including STP while such polymer is seeking a lower level of free energy.